Control Group (QI) Subjects in the QI group will always be advised to quit immediately rather than to quit progressively. Subjects will receive a brief advice on quitting with a warning message similar to subjects in the QP group. In addition, subjects will receive a self-help quitting pamphlet published by the Hong Kong Council on Smoking and Health (COSH). Unlike the QP group, subjects in the QI group will not receive smoking reduction intervention and leaflet, and "booster" intervention during telephone follow-ups. However, they will undergo a similar schedule of telephone follow-up as those in the QP group.